By Martin Plaut
BBC Africa editor
Pretoria previously engaged Zimbabwe in "quiet diplomacy"
There has been an unprecedented international reaction to the beatings inflicted by the Zimbabwe police on members of the opposition - including the leader of the Movement for Democratic Change, Morgan Tsvangirai.
The United States condemned the action as ruthless and repressive, while the British government called for a ratcheting up of pressure on officials close to President Robert Mugabe.
And the chairman of the African Union, Ghanaian President John Kufuor, assured an audience in London that the AU was trying hard to resolve the crisis.
"I want to tell you straight away that I know that the AU is very uncomfortable. The situation in [Zimbabwe] is very embarrassing," Mr Kufuor said.
But the most significant change has come from the South African government.
Mr Mugabe is used to criticism from Europe and the US - and routinely ignores it.
But the tone adopted by his friends in the South African government is entirely new. After years of fending off international pressure, saying they were engaged in what was termed "quiet diplomacy" to persuade Mr Mugabe and the opposition to resolve their differences, the South African authorities have now come out in open opposition to the repression in Zimbabwe.
Deputy Foreign Minister Aziz Pahad called on Harare to respect the rule of law and the rights of all political parties.
But it now emerges that South African President Thabo Mbeki began taking a tougher line over Zimbabwe even before Sunday's beatings.
Zimbabwe's police crackdown has led to protests in South Africa
Mr Mbeki and Mr Mugabe met during last week's independence celebrations in Ghana. Mr Mbeki is reported to have said that he was determined that South Africa's hosting of the Football World Cup in 2010 should not be disrupted by controversial presidential elections in Zimbabwe.
Mr Mugabe had been hoping to postpone the elections until then, to give himself more time in office.
Then on Monday a key Mugabe ally, Zanu party spokesman Nathan Shamuyarira, was called in by leading members of South Africa's governing party - the African National Congress (ANC).
From all reports he was left in no doubt about the displeasure felt by the ANC over the beatings inflicted on Mr Tsvangirai and his followers.
Intense international activity is now under way on how to increase the pressure on Mr Mugabe not to extend his presidency beyond next year.
Britain, the EU and the US are considering what steps should be taken next.
The British government has called for what it describes as a "ramping up" of the European travel ban and asset freeze on 125 senior Zimbabwean officials. This could include extending the measure to the families of those officials already on the list.
This would be particularly aimed at preventing the sons and daughters of cabinet members and senior members of the security forces from studying at European and American universities - something that causes deep resentment in Zimbabwe, where schools and universities are close to collapse.